Distribution of light produced by a light source can be important or even critical in some applications. The light source can be, for example but not necessarily, a light emitting diode “LED”, a filament lamp, or a gas-discharge lamp. FIG. 1 shows a section view of an exemplifying device 101 according to the prior art for modifying the distribution of light produced by a light source 102. The section plane is parallel with the xz-plane of a coordinate system 199. The device 101 comprises a transparent body 103 that is made of transparent material such as for example acrylic plastic, polycarbonate, optical silicone, or glass. The transparent body 103 can be rotationally symmetric with respect to a geometric line 125. It is, however, also possible that the transparent body 103 has a non-circular shape when seen along the z-axis of the coordinate system 199. The transparent body 103 comprises a first surface 104 that acts as a light ingress surface, a second surface 105 that acts as a light egress surface, and a third surface 106 that constitutes a zone around the first surface and joins the first surface. The second 105 surface is configured to reflect, towards the third surface 106, at least a part of light received via the first surface from the light source 102. The third surface 106 is configured to reflect, towards the second surface 105, the light reflected from the second surface so that the light penetrates the second surface 105. In FIG. 1, some of the light beams produced by the light source 102 are depicted with dashed line arrows.
In many cases, there is a need to design a device of the kind illustrated in FIG. 1 so that a combination of a light source and the device produces a desired illumination pattern on a surface being illuminated. For example, there might be a desire to avoid ring-shaped areas having higher and lower light intensities in the above-mentioned illumination pattern. An inherent challenge related to devices of the kind illustrated in FIG. 1 is that the above-mentioned second and third surfaces 105 and 106 have to be shaped so that the condition for total internal reflection “TIR” is fulfilled at all locations on the third surface 106 because light should not leak out through the third surface 106. This requirement limits the freedom to design the shapes of the second and third surfaces 105 and 106, and thereby there may be a need for compromises.